Patriots tight end Rob Gronkowski is having surgery for a herniated disk in his back, a person with knowledge of the details tells The Associated Press.

The person spoke Thursday on condition of anonymity because the surgery has not yet been announced by the team. The surgery was first reported by the Buffalo News.

Gronkowski sat out practice Wednesday with what listed as a back injury. He was absent from practice again on Thursday.

The injury is believed to have occurred during the Patriots' loss to the Seahawks on Nov. 13, in which Gronkowski said he received "probably one of the hardest I've got hit in my career" from safety Earl Thomas.

Gronk sat out the following week against San Francisco. He played part of the first half last week in New England's win over the New York Jets, but did not make a reception.

Gronkowski has missed three games this season. He has 25 catches for 540 yards and three touchdowns.